1. Technical Field
The present invention relates generally to cellular wireless communication systems; and more particularly to the transmission of high-speed data communications in cellular wireless communication systems.
2. Related Art
Cellular wireless communication systems support wireless communication services in many populated areas of the world. While cellular wireless systems were initially constructed to service voice communications, they are now called upon to support data communications as well. The demand for data communication services has exploded with the acceptance and widespread use of the Internet. While data communications have historically been serviced via wired connections, wireless users are now demanding that their wireless units also support data communications. Many wireless subscribers now expect to be able to “surf” the Internet, access their email, and perform other data communication activities using their cellular phones, wireless personal data assistants, wirelessly linked notebook computers, and/or other wireless devices. The demand for wireless system data communications will only increase with time. Thus, wireless systems are currently being created/modified to service these burgeoning data communication demands.
Significant performance issues exist when using a wireless system to service data communications. Wireless systems were initially designed to service the well-defined requirements of voice communications. Generally speaking, voice communications require a sustained bandwidth with minimum signal-to-noise ratio (SNR) and continuity requirements. Data communications, on the other hand, have very different performance requirements. Data communications are typically bursty, discontinuous, and may require a relatively high bandwidth during their active portions. To understand the difficulties in servicing data communications within a wireless system, consider the structure and operation of a cellular wireless system.
Cellular wireless systems include a “network infrastructure” that wirelessly communicates with wireless subscriber units within a respective service coverage area. The network infrastructure typically includes a plurality of base stations dispersed throughout the service coverage area, each of which supports wireless communications within a respective cell (or set of sectors). The base stations couple to base station controllers (BSCs), with each BSC serving a plurality of base stations. Each BSC couples to a mobile switching center (MSC). Each BSC also typically directly or indirectly couples to the Internet.
In operation, a wireless subscriber unit communicates with one (or more) of the base stations. A BSC coupled to the serving base station routes voice communications between the MSC and the serving base station. The MSC routes the voice communication to another MSC or to the public switched telephone network (PSTN). BSCs route data communications between a servicing base station and a packet data network that may couple to the Internet.
The wireless link between the base station and the wireless subscriber unit is defined by one of a plurality of operating standards, e.g., AMPS, TDMA, CDMA, GSM, etc. These operating standards, as well as new 3G and 4G operating standards, define the manner in which the wireless link may be allocated, setup, serviced and torn down. These operating standards must set forth operations that will be satisfactory in servicing both voice and data communications. Each of these next generation systems will be called upon to support high-speed data communications.
CDMA systems are interference limited. Thus, as the number of users serviced by a cell or sector increases, the effective data rate that may be provided to each user decreases. Generally speaking, the data rate that may be supported for any particular user is directly related to the signal quality that may be provided to the user. The signal quality that may be provided to a particular user is typically characterized as the signal- to noise ratio of the user's received signal, i.e., carrier-energy to Noise (Eb/No). In order to provide a higher data rate to a particular user, the user may be allocated a higher transmit power to support higher symbol rates. However, the higher transmit power signal intended for the particular user appears as noise to other users, thereby decreasing the signal quality (Eb/No) of the other users.
A need therefore exists to increase the data throughput provided by a cellular wireless system without increasing the transmit power required for serviced data transmissions.